Shipboard point defense system and elements therefor

ABSTRACT

A combined defense and navigational system on a naval vessel is disclosed. The disclosed system includes a track-while-scan pulse radar which is controlled to provide either navigational information or tracking information on selected targets. Additionally, the disclosed system includes a plurality of guided missiles, each of which may be vertically launched and directed toward intercept of a selected target either by commands from the track-while-scan radar or from an active guidance system in each such missile.

CROSS-REFERENCE TO RELATED CASES

This is a continuation of application Ser. No. 05/823,887, filed Jul.28, 1977 now abandoned.

BACKGROUND OF THE INVENTION

This invention pertains generally to defense systems for naval vesselsand particularly to systems of such type which use radar-guided missilesto intercept and to destroy attacking aircraft or missiles and, inaddition, may be used to detect and to track surface targets such asother naval vessels and navigational aids.

With the continued development of aircraft and missiles, along with moreefficient tactics, a satisfactory solution to the problem of providing adependable air defense system against aircraft and missiles has becomemore and more difficult to attain. In particular, when it is desired toprovide a so-called “point defense” system for a naval vessel, it is nowimperative that provision be made for the capability of modern aircraftand missiles to operate at high speed at very low altitudes. Further, itis imperative that such a defense system be effective when a navalvessel is under attack, either simultaneously or in rapid succession, bya number of aircraft or missiles. In such a situation, provision must bemade in the air defense system to allow detection and tracking to becarried out effectively regardless of the number of attacking aircraftor missiles and the approach path of each such aircraft or missile.

As is very well known, uncontrollable interference effects (which almostinvariably cause either, or both, a reduction in the range at which anairborne target may be detected or an error in the elevation angle ofsuch a target) are experienced when a ship-borne radar is used to detectaircraft or missiles at low elevation angles over the sea. Therefore,one tactic which modern aircraft and missiles may easily and effectivelyfollow is to attack while flying at very low altitude, where theeffectiveness of any known radar-controlled point defense system is aminimum. It is, therefore, manifest that known radar guidance techniquesmay not always be successfully used and that improved radar guidancetechniques, such as one using an active guidance system in anintercepting missile, must be used to attain the desired high degree ofeffectiveness.

Although the general principles underlying active radar guidance systemshave been known for many years, the implementation of any such system ina practical air defense system for a naval vessel has heretofore posedthe almost insuperable problem of providing a dependable, lightweightradar transmitter in a missile. The weight of electron discharge devices(along with the requisite high voltage supplies for such devices) andthe fragility of electron discharge devices have made it impractical,except in special circumstances, to use any such device in a smallmissile suitable for the point defense mission.

It has been proposed to use solid state devices, such as IMPATT diodes,to generate the radio frequency energy required in the transmitter of aradar in an active guidance system in a missile. While such devices arelight, dependable and require relatively small power supplies, theirpower outputs are extremely low. It is necessary, therefore, that thepower outputs of many solid state devices be combined if a useful amountof radio frequency power is to be attained. While basic techniques forcombining the radio frequency outputs of devices such as IMPATT diodesare well known, no technique has yet been developed which would allowefficient use of such devices in a pulse Doppler radar in a missile. Insuch an application, where pulse lengths may be in the nanosecond range,the known basic techniques (developed for continuous wave operation)referred to above are insufficient in themselves to overcome effects oftransients and to provide pulses at predetermined frequencies.

Another basic difficulty in providing a point defense system for a navalvessel derives from the fact that the “reaction time” (meaning theinterval between detection of an attacking aircraft or missile andlaunch of an intercepting missile toward such aircraft or missile) ofsuch a system must be extremely short to allow any possible threat to bemet. A short reaction time makes it feasible to reduce the weights andsizes of the elements, such as the radar and the intercepting missiles,used in the system.

The factor limiting reaction time is the time taken actually to launchan intercepting missile on course to intercept. Unfortunately,conventional launching techniques (where intercepting missiles aremounted on launchers which are designed to be trained to align theintercepting missiles with the desired initial flight paths of suchmissiles) are too slow in operation and too heavy for smaller navalvessels. Further, known launchers cannot practicably be located to havean omnidirectional field of fire. This means that it is quite likelythat a violent maneuver immediately after launch (when aerodynamicforces acting on the control surfaces of an intercepting missile arerelatively weak) is needed to place an intercepting missile in thecorrect flight path toward an attacking missile. Any such maneuver is,of course, extremely wasteful of fuel and is, therefore, to be avoidedif at all possible.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems in the art as it now exists,it is a primary object of this invention to provide an improved pointdefense system for a naval vessel, such system utilizing an activeradar-controlled missile and a radar adapted to detect and track aplurality of airborne targets, such as aircraft or missiles, whethersuch targets are at low or high altitudes.

Another object of this invention is to provide an improved point defensesystem for a naval vessel, such system having a short reaction time sothat an intercepting missile may be launched within a few seconds afterdetection of an attacking aircraft or missile, thereby to overcome anytactical advantage attained by an attacking aircraft or missile duringthe initial stage of an engagement.

Another object of this invention is to provide an improved point airdefense system for naval vessels of any size, such system beingcharacterized by the fact that each one of the intercepting missilesused in such system is vertically launched before ignition of its rocketmotor to provide an omnidirectional field of fire for all such missilesand, further, that initial maneuvering is effected, upon ignition of therocket motor, by thrust vector vanes in the jet stream of the rocketmotor.

Another object of this invention is to provide, in a system of the typecontemplated herein, a capability to detect and track surface targets sothat the system may be used to navigate a naval vessel in restrictedwaters or to detect and track friendly or hostile ships.

GENERAL

The objects of this invention are generally met in a defense system fora naval vessel by providing:

(a) a “track-while-scan” pulse radar, such radar emitting a beam whichis mechanically scanned in azimuth and electronically scanned inelevation to allow a plurality of airborne or surface targets to bedetected and tracked, the frequency of the pulses transmitted by suchradar being varied in accordance with a predetermined program to reducethe deleterious effects of interference from the surface of the sea;

(b) a radar control unit, selectively responsive to command signals froman operator or to signals from the pulse radar, to cause the scanningpattern of the beam from the pulse radar to be changed according to thetactical situation and the signals out of the receiver of the pulseradar to be processed to derive input signals for a control computer;

(c) a control computer programmed to respond to input signals from thepulse radar to differentiate between targets which pose a threat andother signals and to produce control signals which are effective either

(i) to effect tracking of any targets which pose a threat and to launchany one, or ones, of a number of missiles toward any such targets, or

(ii) to allow navigation of the naval vessel, and

(d) a number of missiles for launching, each one of such missiles beingan active radar-guided missile which is vertically launched to have ashort reaction time and which is adapted either to intercept anattacking aircraft or missile flying at any altitude above the sea or tobe directed toward a surface vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference is nowmade to the following description of a preferred embodiment of thisinvention as illustrated in the accompanying drawings, wherein;

FIG. 1 is a sketch showing the different ways in which the contemplatedsystem may be operated in different tactical situations;

FIG. 1A is a sketch showing the elevational cross-sections of the maincontemplated shipboard radar;

FIGS. 1B and 1C are sketches illustrating the pulses of radio frequencyenergy transmitted from the contemplated shipboard radar;

FIG. 2 is a sketch illustrating the various elements making up the radarantenna assembly of the contemplated shipboard radar;

FIG. 3 is a block diagram showing generally the elements in the radarcontrol unit used in the contemplated system;

FIG. 3A is a simplified block diagram of the exciter for the transmitterin the shipboard radar for the contemplated system;

FIGS. 3B and 3C are simplified block diagrams of the monopulse receiverin the shipboard radar for the contemplated system;

FIG. 4 is a generalized block diagram of an intercepting missile to beused in the contemplated system;

FIGS. 4A and 4B are a generalized block diagram of the seeker in themissile shown in FIG. 4 including a simplified block diagram of thereceiver/processor used in such seeker;

FIG. 4C is a simplified block diagram of the phase lock loop shapingnetwork used in the receiver/processor shown in FIGS. 4A and 4B;

FIGS. 5 and 5A are views showing how the contemplated actuators arearranged in the missile and elements of such actuators; and

FIGS. 6 and 6A are sketches showing the elements of the missilelaunching station in the contemplated system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before a detailed description of a preferred embodiment of thecontemplated defense system and of the major components of such systemis undertaken, it will be helpful to enumerate some of the controllingconcepts on which the design of the present system (and componentstherefor) is based. Thus, because the contemplated defense system is tobe used primarily as a point defense system on naval vessels againstattacking aircraft or missiles which are capable of operation atextremely low altitudes, and, secondarily, is to be used against otherthreats and as a navigational aid, the following concepts areincorporated in the system to be described.

(1) Because the range at which aircraft or missiles flying at extremelylow altitudes may be detected by a shipboard radar is primarilydependent upon the frequency of the radar and operational conditions(such as sea state or the presence of land masses), and because acapability to track a large number of simultaneously attacking aircraftor missiles must be provided, an X-band radar with frequency agility andmoderate power, using what may be termed a “track-while-scan” (TWS)technique, is used as the shipboard radar in the system;

(2) Because a capability must be provided to allow many attackingaircraft or missiles to be intercepted under any operational conditions,an active radar guidance technique is preferred in the seeker in theintercepting missiles contemplated for the system;

(3) Because execution of a successful intercept ordinarily may have tobe accomplished in a rather short period of time, the “reaction time”(meaning the interval of time between detection of an attacking aircraftor missile and launching of an intercepting missile toward such aircraftor missile) of the contemplated system is extremely short;

(4) Because the contemplated defense system is to be installed on smallnaval vessels where space is at a premium, the system is also adapted tobe used to detect and track surface vessels as well as aircraft andattacking missiles and, in addition, to be used in navigation of thenaval vessel on which such system is installed.

Referring now to FIG. 1, an assumed tactical situation illustratinggeneral features of the contemplated defense system is shown. Forconvenience, the reference lines (from which the elevation angles to theillustrated airborne targets are measured) are shown to lie in differentplanes. FIGS. 1A through 1C are sketches showing how a radar on a navalvessel 100 (FIG. 1) may be operated in the defense system of FIG. 1. Theequipment making up the contemplated defense system will be illustratedand described in detail hereinafter.

Thus, in FIG. 1, the naval vessel 100 is shown to have installed thereona radar antenna assembly 102, a weapon control center 104, and a missilelaunching station 106 which are inter-connected in a conventional mannerto make up the contemplated defense system.

The radar antenna assembly 102 is mounted on a pedestal (not numbered)in any convenient location on the naval vessel 100 (preferably near theweapon control center 104 to reduce the length of the run of theinterconnections between the radar antenna assembly 102 and the weaponcontrol center 104) so that rotatable antennas (not shown in FIG. 1) maybe continuously scanned in azimuth (here at a rate of 360° per second).One of the rotatable antennas (hereinafter referred to as the radarantenna) is a planar array of antenna elements which may beelectronically scanned in elevation as desired. It will be appreciatedthat scanning in elevation is effected in accordance with commands fromthe weapon control center 104, as modified by signals from attitudesensors, i.e. pitch and roll sensors (not shown), on the naval vessel100. Therefore, as the radar antenna is continuously scanned in azimuth,the elevation angle of the beam from such antenna (relative to anyconvenient reference as, for example, the plane defined by the radarhorizon) may be changed in accordance with any desired program to effecta search in three dimensions for (i) airborne targets (such as theattacking missile 108 or an aircraft 110) at any elevation angles withinany selected range of elevation angles, (ii) for seaborne targets (suchas a ship 112 or a buoy 114) or (iii) other targets (such as a land mass116). An exemplary search program which concentrates on the detection ofattacking missiles at low altitudes yet allows the detection of othertypes of targets is shown in TABLE I below:

TABLE 1 (C) AZIMUTH 1 2 3 4 5 6 7 8 9 10 SCAN NO. BEAM 1A 2A 1A S 1A 3A1A 4A 1A 5A (FIG. 1A) PULSE 7/6.3 7/6.3 7/6.3 2.33 7/6.3 7/6.3 7/6.37/6.3 7/6.3 7/6.3 REPETITION FREQUENCY (KHz) WAVEFORM 1B 1B 1B 1C 1B 1B1B 1B 1B 1B (FIGS. 1B, 1C)

From TABLE I it may be seen that, in each successive group of tencomplete azimuth scans (each of which here is accomplished in onesecond) of the radar antenna, beam 1A (FIG. 1A) is propagated duringfive azimuth scans and each one of the other beams (beams 2A, 3A, 4A, 5Aand S (in FIG. 1A) is propagated during one azimuth scan. As shown inFIG. A, beam 1A here has a beamwidth, in elevation, of 4°(approximately). The other beams (beams S, 2A, 3A, 4A, 5A) havebeamwidths, in elevation, and beam elevation angles as shown in FIG. 1A.It will be appreciated that the search program of TABLE I may be changedwithout departing from the inventive concepts.

The row labeled “PULSE REPETITION FREQUENCY (KHz)” in TABLE I showsthat, whenever beams 1A, 2A, 3A, 4A, 5A are propagated, a staggeredpulse repetition frequency is used. As is well known, a staggered pulserepetition frequency eliminates “blind speeds” in a Doppler radar andallows “multiple time” echo signals to be distinguished from echosignals from targets of interest. The row labeled “WAVEFORM” in TABLE Ishows that, whenever beams 1A, 2A, 3A, 4A, 5A are propagated, eachradiated pulse is made up of two substantially equal subpulses (asindicated in FIG. 1B) and that, whenever beam S is being propagated,each radiated pulse is made up of a relatively long subpulse and arelatively short subpulse. Finally, as indicated in TABLE II below, thefrequencies of the transmitted signals are changed whenever the azimuthof the beam changes by an angle equal to one-half beamwidth.

TABLE 11 (C) FREQUENCY (MHz) 1st Subpulse 8620 8660 8700 . . . 8940 89802nd Subpulse 9020 9060 9100 . . . 9340 9380

The frequency diversity between subpulses along with the frequencyagility between bursts of pulses and the elevation angle of beam 1A areeffective to reduce the effects of reflections from the surface of thesea. Thus, if it be assumed that: (a) the beamwidth, in azimuth, of beam1A is approximately 2°; (b) the pulse repetition frequency is staggeredbetween 7 KHz and 6.3 KHz; and, (c) the scan rate, in azimuth, is360°/sec., then, when beam 1A is propagated:

1. The main lobe of beam 1A is elevated to such extent that the surfaceof the sea may be illuminated, and echo signals reflected off thesurface of the sea may be received only through the sidelobes of suchbeam;

2. Even a small target at low altitude (such as the attacking missile108 (FIG. 1) within the main lobe of beam 1A is illuminated by a number(approximately sixteen to eighteen at a minimum) of successive pulses asthe beam moves in azimuth; and

3. The electrical length of the path of echo signals reflected off thesurface of the sea is changed from subpulse to subpulse as well as fromburst to burst;

It follows that, even in the worst case, i.e. when the sea is calmenough to allow specular reflection to take place: (a) the amplitude ofecho signals (sometimes referred to as multipath signals) from anytarget at a low altitude reflected off the surface of the sea is lowerthan the amplitude of echo signals (sometimes referred to as directsignals) directly reflected from such a target; and (b) the differencein phase between direct signals and multipath signals changes fromsubpulse to subpulse and from burst to burst, making it unlikely thatcompletely destructive interference between such signals may beexperienced during any given azimuth scan.

It will be observed that tracking of different targets could possibly beaccomplished without changing the search pattern shown in TABLE I.However, the interval between successive “updates” of the trackinginformation for any particular target would be dependent upon theelevation angle of each target. That is to say, if tracking of adetected target were to be attempted without changing the search patternshown in TABLE I, updates of the tracking information for a detectedtarget in beam 1A would occur at two second interval and, for a detectedtarget to any other beam, of ten second intervals.

While some noncrucial tactical situations may exist in which theintervals between updates of tracking information may be as just notedabove, it is evident that in crucial tactical situations, e.g. when adetected target has not been identified or when an attack is actuallybeing mounted by an aircraft or missile, the interval between successiveupdates of tracking information should be as short as possible. One wayto effect such an end, while still maintaining a search for new targets,is to cause the search program shown in TABLE I to be interrupted eachtime the azimuth angle of a detected target is approached so that thebeam may be steered to the elevation angle of such target during eachazimuth scan until illumination of the target is completed. After that,the beam would, of course, be steered (in elevation) to resume thesearch program. It will be apparent, then, that the interval betweensuccessive updates of the tracking information for any detected targetwould then be one second, regardless of the elevation angle of suchtarget. With such a modification of the search program it would beextremely unlikely that any detected target would be lost, even onewhich may undertake violent evasive maneuvers at high speed.

A one second interval between successive updates of tracking informationof an intercepting missile is here contemplated. Thus, whenever anintercepting missile is launched to follow a predetermined initialcourse, the position of such missile relative to the naval vessel fromwhich it was launched may be calculated continuously. To transmitmidcourse uplink messages to the intercepting missile the beam isspoiled to allow for the uncertainty in the elevation angle of suchmissile. The beam spoiling occurs only for two very short intervalsequivalent to a very small fraction (less than ten percent) of anantenna dwell time (azimuth beamwidth 2° divided by scan rate 360° persecond). In order then to transmit commands at reasonable intervals tothe intercepting missile during the midcourse phase of flight, it ishere contemplated that the search pattern be interrupted during eachazimuth scan at each such calculated azimuth during the midcourse phaseof flight.

Other tactical situations may exist under which the search program setforth in TABLE I need not be modified to obtain adequate trackinginformation. For example, once a detected target has been identified asa friendly vessel or aircraft, or once a detected target has beenidentified as a navigational aid, it may not be essential to reduce theinterval between successive updates of tracking information.

Referring back again in particular to FIG. 1, the attacking missile 108(after detection at the point marked “DETECTION POINT (AM)”), is shownto be directly closing on the naval vessel 100 along a path marked“FLIGHIT PATH OF ATTACKING MISSILE.” The elevation angle (EL(AM)) of theattacking missile 108 is shown to be less than 4°. Obviously, then, theattacking missile 108 is illuminated by either beam 1A or beam S (FIG.1A). Equally obviously, the actual elevation angle of the attackingmissile 108 cannot be measured with a high degree of precision from thenaval vessel 100.

An intercepting missile 118 from the naval vessel 100 is shown to beentering the terminal phase of flight toward the attacking missile 108.The intercepting missile will be described hereinafter. Suffice it tosay here that in the terminal phase of flight the intercepting missile118 is under the control of an active radar seeker. Such seeker hereincludes a pulse radar transmitter and a monopulse receiver with acommon gimballed antenna for tracking the attacking missile 108 todetermine, in a conventional manner, the “line-of-sight error rate”between the intercepting missile 118 and the attacking missile 108. Sucha rate then is used to control the flight path of the interceptingmissile 118 to the point marked “INTERCEPTION POINT” where a warhead inthe intercepting missile 118 is detonated to destroy the attackingmissile 108. It will be observed that, in the exemplary tacticalsituation being described, the path of the intercepting missile 118 inthe terminal phase is from above the attacking missile 108. Such acourse increases the grazing angle of the beam from the interceptingmissile 118 to such an extent that multipath reflections from theattacking missile 108 are of little moment, regardless of the sea state.

The prior phases of flight of the intercepting missile 118 are indicated“LAUNCHING PHASE” and “MIDCOURSE PHASE”. In the former phase, theintercepting missile 118 is, in accordance with command signals from theweapon control center 104, first selected from among the interceptingmissiles at the missile launching station 106 and then launched (herepneumatically in a direction normal to the plane of the deck of thenaval vessel 100). After the intercepting missile 118 is clear of thenaval vessel 100 the rocket motor (not shown) in the interceptingmissile 118 is ignited. After the rocket motor is ignited, theintercepting missile 118 is first directed toward the flight path to betaken in the midcourse phase of flight (either by vanes in the exhaustof the rocket motor or by control wings) in accordance with commandsfrom the weapon control center 104 stored in an on-board computer priorto liftoff. It will be appreciated that compensation for factors such asthe cant of the deck of the naval vessel 100 at liftoff and the strengthand direction of the apparent wind may be easily effected by modifyingthe commands to the intercepting missile 118 prior to liftoff.

It will also be observed that the azimuth angle of the interceptingmissile 118 during the midcourse phase of flight is offset (as indicatedby the angle marked AZ(OFFSET) from the azimuth angle of the attackingmissile 108. Such offset allows the search pattern to be interruptedduring each scan to update tracking information on both the interceptingmissile 118 and the attacking missile 108. With the rate of receipt oftracking information of both such missiles at a maximum, the bestpossible estimates of any errors in the flight path of the interceptingmissile 118 and the orientation of the gimballed antenna in such missilemay be made on board the naval vessel 100. Commands to reduce sucherrors to a minimum are then transmitted to the intercepting missile118.

It is here noted that it may be possible (when, for example, theapproach of an attacking aircraft or missile is made at a low altitudeover a land mass) for the range to the detection point be very short. Insuch a situation, there would not be sufficient time to execute themidcourse phase just described. Therefore, according to the concepts ofthe contemplated air defense system, when detection occurs at arelatively short range, only the launching and terminal phases arecommanded. This means that the orientation of the gimballed antenna inthe selected intercepting missile is set prior to launch and no offsetangle is commanded. A similar situation, of course, may exist for thesecond intercepting missile if the so-called “shoot-look-shoot”procedure is used against an attacking aircraft or missile which isinitially detected at a relatively long range.

To complete the description of the exemplary tactical situation shown inFIG. 1 the rationale of beam S will be explained. Thus, it will be seenin FIG. 1 that the maneuvering room for the naval vessel 100 isrestricted by the land mass 116 and the buoy 114 marking an underwaterobstruction of some kind. Further, at a relatively long range, the ship112 (here assumed to be hostile) is a threat. Referring to FIG. 1C, itmay be seen that each pulse transmitted in beam S is made up of twosubpulses of different frequencies and length. Further, referring toTABLES I and II, it may be seen that the pulse repetition frequency(when beam S is being propagated) is 2.33 KHz and that “pulse-to-pulse”frequency diversity exists in the same way as for beam 1A. Theseparameters then extend the nonambiguous range, concentrate the greaterpart of the power in each pulse in one subpulse to extend the range ofdetection, provide a means for more precise ranging on targets at shortrange and, finally, reduce the effects of sea echo. The result is thatthe precision of ranging on surface targets at long range (such as theship 112) and on surface targets at short range (such as the buoy 114and points on the land mass 116) may be selected to meet circumstances.Obviously, any conventional filtering technique may be used to allowonly echo signals derived from the narrower subpulse in each pulse to beeffective in ranging on targets such as the buoy 114 or points on theland mass 116.

Before referring specifically to FIG. 2, it should be realized that, forconvenience, the elements making up the radar antenna assembly 102 havebeen shown in a fashion which illustrates the functional features ofsuch elements rather than their physical features. Such an approach hasbeen taken because, it is felt, the constructional details of thevarious elements in the radar antenna assembly 102 and the way in whichsuch elements are mounted will become obvious to a man of skill in theart as the explanation of FIG. 2 proceeds.

With the foregoing in mind it may be seen in FIG. 2 that there are twoantennas (a planar array antenna 201 and an IFF antenna 203) in theradar antenna assembly 102, such antennas being disposed within a commonradome 207 affixed to a rotating platform 209. The latter is rotatablymounted (by means of bearings, not numbered) on a pedestal (portions ofwhich are indicated in FIG. 2 and designated by the numeral 211). Inoperation, then, the rotating platform 209 is continuously rotated by anazimuth drive motor 213 through a platform drive mechanism 215 of anyconventional construction. It follows that, with a rotational speed ofone revolution per second, the planar array antenna 201 and the IFFantenna 203 each complete a complete azimuth scan of 360° in one second.

The planar array antenna 201 here is an array of 1792 dipole elements(not shown) divided between 28 identical horizontally oriented striplinecircuits (not shown) stacked vertically. Each one of the 28 striplinecircuits in turn is connected to dipole elements disposed to producehorizontally polarized radiations at X-band (8.6 to 9.4 GHz). The planararray antenna 201 may, therefore, be deemed to consist of 64 columns ofdipole elements and 28 rows of dipole elements. With appropriatetapering of the radio frequency power applied to the dipole elements,the angular dimensions (two way) of the beams at the various elevationangles are, in azimuth 2° and, in elevation programmable from, say, 4°to 15°. The beams are generated and directed by appropriatelycontrolling phase shifters (not shown but which here are conventionaldigital phase shifters) connected in circuit with the dipole elementsand the stripline circuits. Beams S, 1A, 2A and 3A are focused beams,differing only in their elevation angles. Beams 4A and 5A are defocusedbeams (in elevation).

The control signals for the phase shifters are derived from phaseshifter drivers 217 (here there are twenty-eight such drivers, each onedriving the phase shifters in a row thereof). The individual ones of thephase shifter drivers are, in turn, controlled by signals from aserial-to-parallel converter 219 (here twenty-eight registers, eachhaving a capacity to store a digital word ultimately designating thesettings of the phase shifters in each row). The registers in theserial-to-parallel converter are loaded serially through a slip ringassembly 221 from a radar control unit 301 (FIG. 3).

With the face of the planar array antenna 201 tipped so that itsboresight line is inclined at an angle of 15° with respect to therotating platform 209, it will be immediately apparent that, in theabsence of any pitching or rolling of the naval vessel 100 (FIG. 1), thebeam from the planar array antenna 201 may be easily and rapidly scannedelectronically in elevation from say −30° to +60° in elevation withrespect to the radar horizon. Such a capability, then, allowscompensation for pitch and roll of the naval vessel 100 to be effectedsimply by modifying the digital words out of the radar control unit 301(FIG. 3) in accordance with the pitch and roll of the naval vessel 100.

It has been noted hereinbefore that the planar array antenna 201 is usedin a monopulse radar. As is customary in such a radar, signals to betransmitted are passed from a radar transmitter 311 (FIG. 3) through acirculator 223 and an arithmetic unit 225, to the planar array antenna201. Received signals (the sum signals and elevation difference signals)are then passed as shown from the planar array antenna 201 to amonopulse receiver 313 (FIG. 3). Appropriate rotary joints 227, 229 areprovided to allow the radar antenna assembly 102 to be rotated inazimuth.

It will be noted here that the use of electronic scanning in elevationallows the elevation angle of any detected target (except one detectedin either beam 1A or S) to be measured to a high degree of precision.Thus, let it be assumed that a target is detected in the sum channel ofthe monopulse receiver 313 (FIG. 3) during a particular azimuth scanwhen, say, beam 3A is being propagated in accordance with the program inTABLE I. At detection, the true azimuth of such target is ascertained byappropriately combining the outputs of a pickoff 230 of an antennabearing position indicator 231 and a ship heading sensor 305 (FIG. 3).At the same time, any imbalance in the elevation difference channel inthe monopulse receiver is also measured. Such signals are stored in theradar control unit 301 (FIG. 3) to provide command signals on the nextfollowing azimuth scans when the true azimuth of the previously detectedtarget is approached (noting that beam 1A is being then propagated ifthe program in TABLE I is being followed) to: (a) cause beam 3A to bepropagated; (b) change the elevation angle of beam 3A to null theelevation difference signal; and (c) return, after scanning through thepreviously detected target, to the program being followed.

It will be recalled from the earlier dissertation that the elevationangle of the centerline of the sum pattern of beam 1A cannot be lessthan one-half the beamwidth of such beam. It follows then that, if theelevation angle of a detected target is less than such minimum angle,there will, almost without fail, be an imbalance in the elevationdifference channels. While such an imbalance cannot be nulled asdescribed in the previous paragraph to allow the elevation angle of adetected target to be determined with the degree of precision inherentin the monopulse technique, it is not essential in this situation todetermine such elevation angle. As long as it is known that a detectedtarget is in the sum pattern of beam 1A the boresight line of an antenna(planar antenna array 407AA in FIG. 4) in the intercepting missile 118(FIGS. 1 and 4) may be directed with a sufficiently high degree ofaccuracy to allow such missile to be launched and to effect a successfulintercept.

Obviously, when a target is detected in beam S alone, there is no needto be concerned with the condition of the elevation difference channel.It will be noted that, in the just described process, any effect of yawon the naval vessel 100 (FIG. 1) is eliminated so the true azimuth ofany detected target may also be determined with a high degree ofprecision by well known centering techniques.

The IFF antenna 203 is preferably mounted so that the centerline of itsbeam is parallel to the boresight line of the planar array antenna 201,the interrogating signals and reply signals fed through rotary joints233, 235, as shown.

Referring now to FIG. 3 it may be seen that the main element in theweapon control center 104 is an element designated as a radar controlunit 301. Such unit is shown to receive various condition indicatingsignals from the elements in the radar antenna assembly 102 (FIGS. 1 and2) and sensing elements (ship roll and pitch sensors 303 and shipheading sensor 305) as well as commands from an operator command panel307. In response to the various condition indicating signals, commandand control signals are generated in the radar control unit 301 to: (a)trigger an exciter 309 (described in more detail in connection with FIG.3A) which, in turn, produces radio frequency signals (here assumedordinarily to be in accordance with the program shown in TABLE II) for atransmitter 311 and local oscillator signals of appropriate frequenciesfor a monopulse receiver 313; (b) produce phase shifter commands for thephase shifter drivers 217 (FIG. 2) to effect the desired scanningprogram (such as the one set forth in TABLE I with modifications asdiscussed hereinbefore for detected targets) even though the navalvessel 100 (FIG. 1) may be pitching and rolling; (c) combine theinformation from the bearing position indicator 231 (FIG. 2) and theship heading sensor 305 to determine the true bearing of the beam fromeither the planar array antenna 201 (FIG. 2) or the IFF antenna 203(FIG. 2); (d) produce control signals for a signal processor 315 (whichis responsive to the signals out of the monopulse receiver 313); (e)produce IFF interrogate command signals for an IFF transponder andprocess any reply; (f) produce control and information signals for adisplay 319, and (g) produce appropriate command signals for the missilelaunching station 106 (FIG. 1) to select and to launch a missile.

It will be appreciated that the radar control unit 301 may be a generalpurpose digital computer. For example, a Raytheon Data Systems ModelRDS-500 may be used.

The transmitter 311 may be conventional although it is preferred that atraveling wave tube, TYPE 751-H, be used as a power amplifier with itsmodulating signals being provided by the exciter 309.

The signal processor 315 preferably is similar to the one shown in U.S.Pat. No. 3,875,391 entitled “Pipeline Signal Processor”, inventorsGerald N. Shapiro and Herbert S. Sobel, which is assigned to the sameassignee as the present application.

Before referring to FIG. 3A in detail, it will be noted in passing thatconventional power dividers are there represented simply as dots in thepaths of the various radio frequency signals, with arrows indicating theinput and output ports of such dividers. It is felt that a man ofordinary skill in the art would know the proper type of power dividerfor each different radio frequency signal.

With the foregoing in mind, it may be seen that the exciter 309comprises circuitry for producing both the coded transmitted signalsshown in FIGS. 1B and 1C and in TABLE II and the requisite localoscillator signals for each different one of the two receiving channelsof the monopulse receiver 313 (FIG. 3).

Referring now to the circuitry shown in the lower right hand part ofFIG. 3A, such circuitry is arranged to provide a selection of one of tenpredetermined frequencies spaced 40 MHz apart in the band from 7440 MHzto 7800 MHz. Thus, a bank of crystal oscillators 320 (there being aseparate crystal oscillator corresponding to a submultiple of each oneof the frequencies in TABLE II) are connected, through selector 322, toa frequency multiplier 324 which produces C-band signals. The selectorswitches 322 are controlled by control signals from the radar controlunit 301 (FIG. 3). A control signal from radar control unit 301 (FIG. 3)is also shown to be applied to sweep circuitry 326, the output of whichis shown to be applied to drive amplifier 327, ultimately to control thefrequency of a C-band voltage controlled oscillator 328 (hereinaftersometimes referred to simply as VCO 328). A portion of the output signalfrom VCO 328 is applied through 90° phase shifter 329 to phase detector325. The second input signal to phase detector 325 is provided fromfrequency multiplier 324.

It will now be recognized by those of skill in the art that frequencymultiplier 324 serves as a reference frequency generator to control thefrequency of VCO 328 by means of a phase lock loop comprising phasedetector 325, loop drive amplifier 327, VCO 328 and 90° phase shifter329. The requisite frequency agility is realized by first slewing VCO328 to the region of the desired frequency by means of a control signalfrom radar control unit 301 (FIG. 3) being applied via sweep circuitry326 and loop drive amplifier 327 to VCO 328. An identical control signalfrom radar control unit 301 is applied to selector switches 322 therebyselecting the appropriate crystal oscillator from the bank of crystaloscillators 320. To assist in obtaining phase lock between VCO 328 andthe output signal from frequency multiplier 324 (which is determined bythe frequency of the selected one of crystal controlled oscillators 320)sweep circuit 326 slews VCO 328 within the capture range of the phaselock loop, thereby narrowing the capture range for phase lock. A sampleand hold circuit (not shown) within loop drive amplifier 327 senses aphase lock, as indicated by the signal out of phase detector 325, andpositions VCO 328 to that particular frequency as determined from thevoltage out of sweep circuit 326. The sample and hold circuit (notshown) thereby inhibits sweep circuit 326 after acquisition of a phaselock.

The output signal from C-band VCO 328 is applied to mixer 330 to form,in a manner to be described, the X-band frequencies listed in TABLE II.It will be noted here in passing that the same output signal from VCO328 provides the first local oscillator signal (marked L.O. (1) andsometimes so designated hereinafter) to the two receiving channels ofthe monopulse receiver 313 (FIG. 3). With the frequencies of the firstand second subpulses in each transmitted pulse (and in each receivedpulse) differing by 400 MHz as indicated in TABLE II, it is manifestthat heterodyning L.O. (1) with the subpulses in any received pulseresults in two different intermediate frequency signals being formed.Appropriate filtering may then be employed to direct such tointermediate frequency signals into different channels in the monopulsereceiver 313 (FIG. 3).

Exciter 309 is also shown to include a 42.8 MHz crystal-controlledoscillator 331, a 60 MHz crystal-controlled oscillator 332, a 1120 MHzcrystal-controlled oscillator 333 and a 1520 MHz crystal-controlledoscillator 334, all of which are of conventional design, and arearranged in a manner to be described, to provide first and secondsubpulses at frequencies of 1180 MHz and 1580 MHz, respectively. Theoutput signal from the 42.8 MHz crystal-controlled oscillator 331 isshown to be split, with a portion being provided to monopulse receiver313 (FIG. 3) as an L.O. (4) signal and a portion being applied to mixer335. The 42.8 MHz signal is heterodyned in mixer 335 with a 60 MHzsignal from a 60 MHz crystal-controlled oscillator 332 to produce a 17.2MHz reference signal which is also sent to monopulse receiver 313 (FIG.3) for reasons which will be explained in greater detail hereinafterwith reference to FIG. 3C. The output signals from the 1120 MHzcrystal-controlled oscillator 333 and the 1520 MHz crystal-controlledoscillator 334 are also shown to be split, with portions thereof beingapplied to monopulse receiver 313 (FIG. 3) as L.O. (2) and L.O. (3)signals, respectively.

Exciter 309 is also shown to include a 1180 MHz voltage controlledoscillator 336 (hereinafter referred to simply as VCO 336) and a 1580MHz voltage controlled oscillator 337 (hereinafter referred to as VCO337). The output signal from VCO 336 is shown to be split, with aportion thereof being applied to mixer 338 wherein it is heterodynedwith a portion of the signal from the 1120 MHz crystal-controlledoscillator 333 to produce a 60 MHz output signal. The 60 MHz signal frommixer 338 is applied to quadrature phase detector 339 wherein it isdetected against a reference signal obtained by passing a portion of theoutput signal from 60 MHz crystal-controlled oscillator 332. The outputsignal from quadrature phase detector 339 is applied via a low passfilter (not shown) and a loop shaping amplifier (also not shown) to VCO336, ultimately to control the frequency of VCO 336. It will now berecognized by those of skill in the art that the just described elementscomprise a phase lock loop to lock the frequency of VCO 336 to that ofthe 60 MHz crystal-controlled oscillator 332.

The output frequency of VCO 337 is controlled in a similar fashion.Thus, a portion of the output signal from VCO 337 is applied to mixer341 wherein it is heterodyned with a portion of the signal from the 1520MHz crystal-controlled oscillator 334 to produce a 60 MHz output signal.Such 60 MHz signal is passed to quadrature phase detector 342 wherein itis phase detected against a reference signal obtained from 60 MHzcrystal-controlled oscillator 332. The output signal from phase detector342 is passed via a low pass filter (not shown) and a loop shapingamplifier (also not shown) to VCO 337 to control the frequency of thatelement.

The output signals from VCOs 336, 337 are also shown to be applied to apair of switches 343, 344, respectively, which are controlled by controlsignals supplied by radar control unit 301 (FIG. 3). In order to formfirst and second subpulses at frequencies of 1180 and 1580 MHz,respectively, radar control unit 301 (FIG. 3) alternately selects, viaswitches 343, 344, the output signals from either VCO 336 or VCO 337.The selected frequency is applied via amplifier 345 to mixer 330 whereinit is heterodyned with the output signal from C-band VCO 328 to form thetransmitted frequencies indicated in Table II. Loads 346, 347 areprovided, as shown, on switches 343, 344 to alternately absorb, inresponse to the control signals provided by radar control unit 301 (FIG.3), the RF energy from VCOs 336, 337. Finally, a switch 348, whichincludes a load (not shown) and which is also controlled by controlsignals from radar control unit 301 (FIG. 3), is included to provide adegree of pulse shaping and also to prevent CW signals from exciter 309from being sent to the transmitter 311 (FIG. 3) during the interpulseperiod.

Before referring to FIGS. 3B and 3C in detail, it will be noted thatconventional power dividers are, again, there represented simply as dotsin the paths of the various radio frequency signals, with arrowsindicating the input and output ports of such dividers. It is felt thatone of ordinary skill in the art would know the proper type of powerdivider for each different radio frequency signal. It is also noted thatmono-pulse receiver 313 is a two-channel device, one channelcorresponding to the lower frequency sub-pulse listed in Table II andthe remaining channel corresponding to the higher frequency sub-pulse inTable II. The letter “L” in a reference numeral is used to designatecomponents in the low frequency channel, while the letter “H” in areference numeral designates a corresponding high frequency channelcomponent.

Referring now to FIG. 3B, monopulse receiver 313 is shown to accept themonopulse sum (Σ) channel signal from circulator 223 (FIG. 2) and theelevation difference channel signal (Δ) from rotary joint 229 (FIG. 2).The Σ and Δ channel signals are downconverted to suitable L-band signalsby being heterodyned in mixers 351Σ and 351Δ, respectively, with theL.O. (1) signal from exciter 309 (FIG. 3A). The L-band Σ channel signalis frequency diplexed into an 1180 MHz signal and a 1580 MHz signal bybeing passed through an 1180 MHz band pass filter 3521, and a 1580 MHzband pass filter 352H. The 1180 MHz and 1580 MHz signals aredownconverted to 60 MHz I.F. signals by being mixed in mixers 353L and353H with the 1120 MHz L.O. (2) and 1520 MHz L.O. (3) signals,respectively, from exciter 309 (FIG. 3A). After suitable amplificationin I.F. amplifiers 354L and 354H, the 60 MHz Σ channel signals arepassed to summing amplifiers 355L and 355H.

The Δ channel signals are also frequency diplexed into two separatechannels by passing such signals through an 1180 MHz band pass filter356L and a 1580 MHz band pass filter 356H. These signals aresubsequently downconverted to 60 MHz I.F. signals by being heterodynedin mixers 357L and 357H with the 1120 MHz L.O. (2) and 1520 MHz L.O. (3)signals from exciter 309, as shown. The 60 MHz Δ channel signals frommixers 357L and 357H are amplified by I.F. amplifiers 358L and 358H,respectively, prior to being downconverted to 17.2 MHz I.F. signals bybeing heterodyned in mixers 359L and 359H with the 42.8 MHz L.O. (4)signal from exciter 309 (FIG. 3A). It is here noted that the 42.8 MHzL.O. (4) signal is applied to mixers 359L and 359H via a switch 360.Switch 360, which is controlled by a signal from radar control unit 301(FIG. 3), is used to gate out the Δ channel information when the radaris in the acquisition mode. The 17.2 MHz Δ channel signals are passedvia 17.2 MHz band pass filters 361L and 361H to summing amplifiers 355Land 355H wherein they are frequency multiplexed with the correspondingfrequencies in the Σ channel. Thus, the 60 MHz Σ channel signal and the17.2 MHz Δ channel signal derived from the 1180 MHz L-band signal arecombined in summing amplifier 355L, while the 60 MHz Σ channel signaland the 17.2 MHz Δ channel signal derived from the 1580 MHz L-bandsignal are combined in summing amplifier 355H. Frequency multiplexingthe Σ and Δ information for each of the dual frequencies into commonchannels enables common processing of the Σ and Δ information throughwideband automatic gain control (AGC) circuitry, thereby minimizing theeffects of relative phase and amplitude variations and minimizing errorsin making elevation angle measurements.

The frequency multiplexed signals out of summing amplifiers 355L, 355Hare passed to AGC amplifiers 362L, 362H which control the dynamic rangeof monopulse receiver 313. Referring now to FIG. 3C, the Σ and Δ signalsfor each of the dual frequencies are separated by passing them through60 MHz band pass filters 363L, 363H and 17.2 MHz band pass filters 364L,364H, as shown. The Σ and Δ signals are subsequently time multiplexed bymeans of passing the Δ channel signals through delay lines 365L, 365H.Time multiplexing permits common analog to digital (A/D) conversion ofthe Σ and Δ channel signals. It is here noted that delay lines 365L,365H are dual delay lines, i.e., delay lines 365L, 365H provide both a7.0 and 21.0 microsecond delay, the proper delay being selected byswitches 366L, 366H, which are controlled by means of a signal providedby radar control unit 301 (FIG. 3). The reason for the dual delay isthat a 7 microsecond range window is utilized in track modes and thesystem must be capable of tracking two targets in the same antenna beamdwell. Thus, if the range difference of the two tracked targets is lessthan 7.0 microseconds or 3500 feet, the 21.0 microsecond delay is usedand the 7.0 microsecond delay line is selected for all other targetrange separations.

The Σ channel signals for each of the dual frequencies are downconvertedto 17.2 MHz signals by being heterodyned in mixers 367L, 367H with the42.8 MHz L.O. (4) signal from exciter 309 (FIG. 3A) to simplify thesubsequent video detection processing. The 42.8 MHz L.O. (4) signal isapplied to mixers 367L, 367H via switch 360 so that the Δ channelinformation may be gated out in the acquisition modes. The 17.2 MHz Σand Δ channel signals for each of the dual frequencies are, after timemultiplexing, combined together in summing amplifiers 368L, 368H.

Before proceeding with a description of the quadrature detectioncircuitry, it is noted that the 60 MHz Σ channel data in each of thefrequency channels is applied to video detectors 369L, 369H. This pairof signals corresponds to Σ channel information at each of the twofrequencies of the dual frequency transmission. In the surface mode ofoperation, as explained hereinabove, the two pulses transmittedcontiguously have pulse widths of 4.1 and 0.1 microseconds,respectively; the former being used for long range, low resolution, andthe latter being used for short range, high resolution. The outputsignals from video detectors 369L, 369H are applied to a switch 370which is used to select either the short or long waveform in response toa control signal provided by radar control unit 301 (FIG. 3). Followingswitch 370 an envelope detector logarithmic amplifier circuit 371 isused, whose output is raw video data which is sent to display unit 319(FIG. 3).

The time multiplexed Σ and Δ channel signals are applied to a pair ofquadrature detection circuits 372L, 372H. It will be appreciated bythose of skill in the art that quadrature detection circuits 372L, 372Hinclude a pair of phase detectors (not shown) fed in phase quadrature bya 17.2 MHz reference signal obtained from exciter 309 (FIG. 3A). Alsoincluded (but not shown) in quadrature detection circuits 372L, 372H arelow pass filters which remove L.O. and other higher order frequencycomponents and DC amplifiers which are used for drive and gain scaling,all of which are of conventional design. The in phase (I) and quadraturephase (Q) components from quadrature detection circuits 372L, 372H aredelayed with respect to each other by passing the Q component fromquadrature detection circuit 372L through a 300 nanosecond delay line373, and the I and Q components from phase detection circuit 372Hthrough 700 nanosecond delay line 374, and 1.3 microsecond delay line375, respectively. The time multiplexed I and Q signals are sent tosignal processor 315 (FIG. 3) wherein they are digitized by a single A/Dconverter (not shown) prior to processing.

Referring now to FIG. 4, it will first be noted that severalsimplifications have been made in the interest of clarity. For example,the interconnections between the various components have not been shownnor have mechanical details such as mounting structures for the variouscomponents. With the foregoing in mind it will be observed that theintercepting missile 118 is here contemplated to be tail-controlled,either by means of vanes 401A, 401B in the exhaust of a rocket motor 402or by tail surfaces 403A, 403B in accordance with control signalsapplied, respectively, to actuators 404A, 404B (it being understood thatanother pair of vanes, another pair of tail surfaces and another pair ofactuators, none of which is shown, are mounted to make a cruciformcontrol arrangement. The control signals to the actuators 404A, 404B arederived, prior to launch, through an umbilical 405 and, after launch,from a seeker and autopilot 407. Suffice it to say here that the seekerand autopilot 407 includes, inter alia, a pulse Doppler radar with amonopulse receiver for use during the terminal phase of flight. The rearreceiver and decoder 406 is used during the midcourse phase of flight toderive target position signals transmitted from the naval vessel 100(FIG. 1) to a rear antenna 406A. Ultimately, then, such signals areconverted in the seeker and autopilot 407 to control signals for theactuators 404A, 404B and a gimballed antenna assembly 407A mountedwithin a radome 408. The latter then is actuated to direct the boresightline of a planar antenna array 407AA toward the attacking missile 108(FIG. 1). (As noted hereinbefore, when the midcourse phase of the flightof the intercepting missile 118 is not to be carried out, the controlsignals for initially directing the planar antenna array 407AA areapplied prior to launch through the umbilical 405.)

A battery 409, a fuze 110, a warhead 111 and inertial instruments 112,all of which here may be of any conventional construction, are alsocarried by the intercepting missile 118. It will now be obvious that theflight path of the intercepting missile 118 may be controlled.

Referring now to FIGS. 4A and 4B, the major components of the seeker andautopilot 407 are seen generally to include a monopulsereceiver/processor 413 RP, a master oscillator 4130, a computer andautopilot 413CA, a synchronizer 414, a transmitter 415 and a circulator416. It will be recognized immediately by those of skill in the art thatthe enumerated major components connected together as shown constitute apulse radar wherein the elements of the seeker and autopilot 407correspond with the elements of known types of semiactive radar guidancesystems. That is to say, the elements of seeker and autopilot 407 may beoperated, if desired, during flight of the intercepting missile 118(FIG. 1) as the missile-borne parts of a semiactive radar guidancesystem using signals derived through the rear receiver and decoder 406(FIG. 4) from, for example, the radar antenna assembly 102 (FIG. 1) toderive the requisite control signals for the actuators 404A, 404B (FIG.4), the gimballed antenna assembly 407A (FIG. 4) and the requisitecontrol signals for the master oscillator 4130 to carry out a successfulintercept of a target such as the attacking missile 108 (FIG. 1).

Briefly, the monopulse receiver/processor 413RP here is responsive to asum signal here derived in a conventional monopulse arithmetic unit, notshown, in the gimballed antenna assembly 407A (FIG. 4) and passedthrough the circulator 416 and two difference signals from thatarithmetic unit. The three radio frequency signals just mentioned aredesignated in FIG. 4A as “Σ”, “ΔA_(z)”, “ΔE_(l)”, meaning, respectively,the sum, azimuth difference and elevation difference signals.

The monopulse receiver processor 413RP passes the ΔA_(z), ΔE_(l) and Σsignals through limiters 417 ₁, 417 ₂ and 417 ₃, respectively, to mixers418 ₁, 418 ₂ and 418 ₃ wherein they are heterodyned with a localoscillator signal (marked f(L.O.)) from master oscillator 4130 anddownconverted to 31 MHz intermediate frequency (IF) signals. Such IFsignals are then amplified by amplifiers 419 ₁, 419 ₂ and 419 ₃ andpassed through blanking gates 420 ₁, 420 ₂ and 420 ₃, which arecontrolled by a control signal from synchronizer 414 to gate offmonopulse receiver processor 413RP when transmitter 415 is gated ON. TheIF signals from blanking gates 420 ₁, 420 ₂ and 420 ₃ are amplified byamplifiers 421 ₁, 421 ₂ and 421 ₃ and then passed through narrow band (1KHz) crystal filters 423 ₁, 423 ₂ and 423 ₃. The Σ channel signal fromblanking gate 420 ₃ is shown to be split into two channels whichhereinafter will be referred to as the “narrow band” (N.B.) Σ signal andthe “wide band” (W.B.) Σ signal. The N.B. Σ signal is the one that ispassed through the narrow band (1 KHz) crystal filter 423 ₃. The W.B. Σsignal after being amplified in amplifier 421 ₄ is passed through a wideband (10 KHz) crystal filter 424. After suitable amplification inamplifiers 425 ₁, 425 ₂ . . . 425 ₄ the filtered IF signals are appliedto time multiplexer 426 wherein they are combined into a single channel,in response to a “MUX” signal from synchronizer 414.

Before proceeding, it is here noted that W.B. Σ signal is used duringacquisition modes of the seeker and autopilot 407, while the N.B. Σsignal is used during the tracking mode. Further, master oscillator 4130in addition to producing the local oscillator signal (f(L.O.)) alsoproduces a signal marked f(T) for the transmitter 415. The frequency ofthe latter signal then differs (when a target such as the attackingmissile 108 (FIG. 1) is being tracked) from the frequency of the localoscillator signal by an amount equal to the center frequency (here 31MHz) of the IF channels in monopulse receiver/processor 413RP plus theDoppler shift due to the range rate between the attacking missile 108(FIG. 1) and the intercepting missile 118 (FIG. 1). Such Doppler shiftis automatically determined in monopulse receiver/processor 413RP in amanner to be described. Suffice it to say here that, when a target isbeing tracked, the frequency of the local oscillator signal, (f(L.O.),is maintained at the proper frequency to compensate for any Dopplershift.

The multiplexed signals from time multiplexer 426 are passed through anAGC amplifier 427, which controls the dynamic range of monopulsereceiver/processor 413RP, to a switch 428, which is shown to becontrolled by a de-multiplex (DEMUX) signal from synchronizer 414.During an acquisition mode the switch 428 is effective to gate only theW.B. Σ signal to power divider 429. A first portion of the W.B. Σ signalfrom power divider 429 is shown to be applied via amplifier 430 to anAGC detector 431. The output signal from AGC detector 431 is passed viaswitch 432 to AGC amplifier 427, as shown. Switch 432 is controlled, ina manner to be described in greater detail hereinafter, by a controlsignal provided by synchronizer 414.

A second portion of the W.B. Σ signal from power divider 429 is passedvia amplifier 433 to a quadrature demodulator (not numbered) comprisinga so-called “in-phase” phase detector 434I and to a so-called“quadrature phase” phase detector 434Q. A pair of quadrature referencesignals, obtained by passing the output signal from a 31 MHz referenceoscillator 435 through a quadrature hybrid 436, is also applied to phasedetectors 434I, 434Q, as shown. The output signals from phase detectors434I, 434Q are sent via amplifiers 437I, 437Q to computer and autopilot413CA. When a phase lock between the W.B. Σ signal and the 31 MHzreference signal from 31 MHz reference oscillator 435 is obtained, theoutput signal from phase detector 4341 is at a maximum and, therefore, aportion of the output signal from phase detector 4341 is applied to acomparator 438 which includes a low pass filter (not shown) to provide aloop lock indicator signal to computer and autopilot 413CA when theamplitude of the signal out of phase detector 437I exceeds that of aD.C. reference. Upon receipt of the loop lock indicator signal thecomputer and autopilot 413CA provides a DESIGNATE ENABLE signal to theloop shaping circuit 439. In the absence of a phase lock, the outputsignal from phase detector 434Q is an indication (in magnitude and sign)of the difference between the W.B. Σ signal and the 31 MHz referencesignal, and is here referred to as the DOPPLER ERROR SIGNAL. The DOPPLERERROR SIGNAL is shown to be applied to loop shaping circuit 439 alongwith other signals to be described to produce a DOPPLER ERROR CONTROLSIGNAL to master oscillator 4130 ultimately to change the localoscillator frequency, f(L.O.), until the DOPPLER ERROR SIGNAL is nulled.The details of the phase lock loop shaping circuit 439 will be explainedin greater detail hereinafter, suffice it to say here that suchcircuitry is effective to expand the capture range of the phase lockloop such that it is not limited by the characteristics of phasedetector 434Q.

While in the acquisition mode, the I and Q data from the quadraturedemodulator (not numbered), which are here video signals having a 5 KHzbandwidth, are fed to a Fast Fourier Transform (FFT) spectrum analyzer(not shown) within the computer and autopilot 413CA. Such a spectrumanalyzer, which as is known is analogous to a filter bank, determinesthe Doppler frequency of a target such as the aircraft 110 (FIG. 1) to afrequency resolution of 200 Hz. Computer and autopilot 413CAcommunicates its estimate of the target frequency, as obtained from theFFT spectrum analyzer (not shown), to the phase lock loop shapingcircuitry 439 as a signal labeled TARGET DESIGNATE. The phase lock loopgain and shaping are such that the loop will lock to a target whosefrequency is within 200 Hz of the designated frequency.

Simultaneously with the transmission of the TARGET DESIGNATE signal tothe phase lock loop shaping circuitry 439, computer and autopilot 413CAtransmits a MODE SELECT SIGNAL to synchronizer 414 which, in turn,generates an ACQ/TRK signal which is effective to switch seeker andautopilot 407 from an acquisition to a track mode. Such ACQ/TRK signalis shown to be applied to the time multiplexer 426 and the switch 432.In the track mode, time multiplexer 426 gates the N.B. Σ and Δ channeldata through the AGC amplifier 427 to switch 428 in such a fashion thaton every other clock pulse from the synchronizer 414 the N.B. Σ data ispresented. Thus, the first clock pulse corresponds to the N.B. Σ dataand the fourth clock pulse corresponds to the ΔA_(z) data. The switch428, in response to the DEMUX signal supplied by synchronizer 414,alternately passes the N.B. Σ channel data to power divider 429 and theΔ channel data to amplifier 440. The power divider 429 splits the N.B. Σsignal and sends a first portion of such signal to the quadraturedemodulator (not numbered but described hereinabove) and a secondportion to amplifier 430, as shown. The 31 MHz Δ channel data fromamplifier 440 is shown to be applied to mixer 441 wherein it isdownconverted to a suitable video frequency signal by being heterodynedwith the N.B. Σ signal in a manner to be described. The N.B. Σ channelsignal from amplifier 430 is passed through a 4 KHz crystal filter 442,a phase trimming network 443 and an amplifier 444 before being appliedto mixer 441. It will now be appreciated by those of skill in the artthat, as the N.B. Σ channel data from amplifier 430 is in the form of apulse (due to the requisite time multiplexing and demultiplexing), whensuch data is passed through the 4 KHz crystal filter 442 a certainamount of ringing will occur. It is this pulse ringing which iseffective to maintain the presence of the N.B. Σ signal at mixer 441while the Δ channel data is being gated through switch 428. The phasetrimming network 443 is provided to maintain the requisite phase balance(match) between the Σ and Δ channels. The Δ channel data from mixer 441is passed via amplifier 443 to switch 446. The switch 446 is controlledby the DEMUX signals from synchronizer 414 and is effective to gate theΔA_(z) data through amplifier 447 and the ΔE_(l) data through amplifier448 to computer and autopilot 413CA wherein such data is converted toyaw and pitch error signals to derive the requisite control signals forthe actuator 404A, 404B . . . (FIG. 4) and the gimballed antennaassembly 407A (FIG. 4).

It is noted here in passing that in the track mode, the switch 432 ispositioned such that the output signal from AGC detector 449 is used tocontrol AGC amplifier 427. As the input signal to AGC detector 449 isobtained from phase trimming network 443 advantage is taken of the pulseringing feature (described above) to present a continuous signal to AGCdetector 449.

The just-described method for downconverting the Δ channel data offersan advantage over more conventional designs wherein a reference signalobtained from the phase lock loop reference oscillator (here masteroscillator 4130) is used to downconvert the Δ channel data. Thus, in achanging environment wherein a “Velocity Gate Pull Off” (VGPO) typejammer can cause a phase lock loop to break lock, the referenceoscillator would not be properly positioned to downconvert the Δ channeldata, thereby giving rise to tracking errors or even resulting in a lossof track, whereas if in the herein contemplated design the N.B. Σchannel signal is used to downconvert the Δ channel data, no suchdistortion or loss of track can result.

Referring now to FIG. 4C, the phase lock loop shaping network 439 isshown to receive both a TARGET DESIGNATE and a DESIGNATE ENABLE signalfrom computer and autopilot 413CA. The TARGET DESIGNATE signal is avoltage initially representative of the expected Doppler frequency of atarget such as the aircraft 110 (FIG. 1) as computed by radar controlunit 301. (FIG. 3). Such signal is supplied to seeker and autopilot 407(FIG. 4A) via umbilical 405 prior to missile launch. The TARGETDESIGNATE signal is then updated by a signal derived in a FET spectrumanalyzer (not shown) within computer and autopilot 413CA (FIG. 4A) andis effective to position the phase lock loop (not numbered but shown inFIG. 4A) to within 200 Hz of the Doppler frequency of the target. TheTARGET DESIGNATE signal is shown to be applied via a switch 451 to anamplifier 452 and a storage capacitor C1. The switch 451 is controlledby the DESIGNATE ENABLE signal, which is effective to open the switch451 once computer and autopilot 413CA receives the loop lock indicatorsignal from the comparator 438 (FIG. 4B).

The output signal from amplifier 452 is passed via a voltage dividercomprising resistors R2 and R3 to amplifier 453. The values of R2 and R3are chosen to offset the gain of amplifier 453 which is determined byfeedback resistors R1 and R9. The gain through amplifier 452 andresistor R2 is unity and, therefore, the voltage V_(DES) appearing atamplifier 453 is identical to that stored in storage capacitor C1. Thesecond input signal to amplifier 453 is the DOPPLER ERROR SIGNALobtained from phase detector 434Q (FIG. 4) via amplifier 437Q (FIG. 4).

The DOPPLER ERROR SIGNAL is shown to be passed via resistors R4 and R5to storage capacitor C2 and to amplifier 454. A feedback voltage isprovided to amplifier 454 from the junction of resistors R6 and R7.Again, the gain through amplifier 454 and resistor R8 is unity and,therefore, the voltage V_(ERR) appearing at amplifier 453 is identicalto that stored in storage capacitor C2. Amplifier 453 provides an outputvoltage V_(D) (or DOPPLER ERROR CONTROL SIGNAL) which is the algebraicsum of the two input voltages V_(DES) and V_(ERR), to the masteroscillator 4130 (FIG. 4A) to change the local oscillator frequency,f(L.O.), ultimately to null the DOPPLER ERROR SIGNAL.

It will now be seen that because of resistor R1 between the output ofamplifier 453 and storage capacitor C1, any voltage difference betweensuch points will cause a current to flow through R1 until equilibriumbetween these points is realized. Once the DESIGNATE ENABLE voltage isapplied to switch 451 an inner loop is formed within loop shapingnetwork 439 by means of resistor R1. The inner loop so formed forcesphase detector 434Q to operate about its null (zero volts output) point.

Referring now to FIG. 5, actuator 404A is shown to include a basketrotor motor 501, a permanent magnet field assembly 503, a harmonic drivegear train 505 (or reduction gear) and a tail surface shaft 507, all ofwhich are integrally mounted and supported, as shown. The actuator 404Ais bolted to a plate 509 which forms a quarter section of the tailsection of the intercepting missile 118 (FIG. 4). The plate 509, whichis bolted to the missile skin 510, has mounted on it a support member523 which will be described in greater detail hereinafter. The actuator404A is concentrically packaged in the annulus between the innerdiameter of the missile skin 510 and the outer diameter of the rocketmotor exhaust tube 511 and, therefore, the overall height of theactuator 404A is kept to a minimum to avoid undesired protuberances inthe missile skin 510. A layer of thermal insulation 512 is provided, asshown, on the rocket motor exhaust tube 511 to prevent damage to theexhaust tube 511. The thermal insulation 512 is shown to have aprotrusion (not numbered) formed therein, such protrusion forming anozzle in the rocket motor exhaust tube 511.

The basket rotor motor 501 is shown to be packaged within an aluminumhousing 521 which is bolted to the plate 509. The basket rotor motor 501utilizes a low inertia, high torque basket rotor 513, which is supportedby an integral hollow shaft 514, which, in turn, is supported by twohigh speed bearings 515. The bearings 515 are supported in an internal,stationary composite structure (not numbered) which includes a highstrength steel tube 516 that supports the outer races (not numbered) ofthe bearings 515. The stationary composite structure (not numbered) issurrounded by a concentric cylinder 517 of a material, here magneticsteel, having a high magnetic permeability and having a high magneticsaturation flux density. Thus, cylinder 517 provides a magnetic returnpath and completes the magnetic path between the motor poles (not shown)through the air gap (not numbered) and the basket rotor 513. A coaxialbrush assembly 519, which is packaged in a phenolic ring 518, is locatedconcentrically between the cylinder 517 and the steel tube 516.

The actual length of the motor 501 is reduced without reducing theeffective motor length by means of folding the end turns (not numbered)at each end of the basket rotor 513. The ends are folded up at the openend and down at the supported end of the basket rotor 513. The use ofthe basket rotor 513 permits the utilization of the space internal tothe basket rotor 513 for purposes other than magnetic return as is thecase with conventional motors. Thus, the spring loaded coaxial brushassembly 519 and a commutator 529 are contained within the basket rotor513, as shown. The requisite electrical contact to commutator 529 isprovided by means of a wire 529 a which is shown to extend from brushassembly 519 through a hole (not numbered) provided in the phenolic ring518, finally to exit at a hole (not numbered) provided on the bottom ofbasket rotor motor 501. Wire 529 a is terminated at a drive amplifier(not shown).

The harmonic drive gear train 505, which is here a part No. 7319020,purchased from United Shoe Machinery Corp., ICON Division, Woburn, Mass.provides the high reduction ratio between the motor 501 and the tail finshaft 507. Briefly, the harmonic drive gear train assembly 505 comprisesthree basic components (none of which are shown), namely a wavegenerator, a circular spline and a dynamic spline. The wave generator isan elliptical hollow plug of titanium onto which a special bearinghaving a flexible outer race is pressed. A flexible spline is pressedover the bearing outer race. The wave generator couples to the motor 501and serves to convert rotation of the motor into a correspondingelliptical motion of the flex spline. The circular spline is an internalspline that is fixed to the housing 521 and serves to transfer the loadsinduced in the flex spline to the housing 521. The dynamic spline is amovable internal spline which is rigidly connected to the tail fin shaft507. The requisite reduction ratio is determined by the number of teethin the dynamic spline as compared with the number of teeth in the flexspline.

The tail fin shaft 507 is supported on the fin end by a duplex ballbearing set 520 which transfers the shear loads due to aerodynamicloading of the tail surface 403A through the support member 523 and theplate 509 to the missile skin 510. It is noted here in passing that,while a single duplex ball bearing set has been shown for the purposesof clarity, in actual practice a pair of duplex ball bearing sets isused. The duplex ball bearing set 520 also absorbs the axial thrustloads on the shaft 507 due to maneuvering of the intercepting missile118 (FIG. 4). A second ball bearing set 524 at the bottom of the tailfin shaft 507 reacts to the bending moment loads on the tail fin shaft507 created by the aerodynamic wind load on the tail surface end inorder to absorb the stresses induced by the high aerodynamic loads onthe tail surface 403A. The tail fin shaft 507 is reduced in diameter atthe lower end because of the reduced stress concentrations in this area,thereby allowing the tail fin shaft 507 to pass through the basket rotormotor 501. The tail fin shaft 507 is isolated from the basket rotormotor 501 so as to not introduce tail surface moments into the motorrotor bearings 515. The tail surface 403A is attached to the tail finshaft 507 in any convenient manner, here by means of a locking pin (notnumbered).

A feedback element (not numbered), which comprises a circular arcplastic potentiometer 525 (sometimes hereinafter referred to simply aspotentiometer 525) and a wiper 526 is included to provide positionalinformation in order to control the actuator 404A. The wiper 526 ismounted to the flex spline (not numbered) and the potentiometer 525 ismounted to the actuator housing 521, as shown. The potentiometer 525 hastwo tracks (not shown), the first one of which is a resistive elementhaving a center tap and two end taps. The center tap is grounded, whilepositive voltage is applied to one of the end taps and a negativevoltage is applied to the remaining end tap. The second track onpotentiometer 525 is a continuous strip of metal. The wiper 526 includestwo arms (not numbered) which are electrically connected together. Thefirst arm of wiper 526 contacts the resistive track (not shown) onpotentiometer 525 and receives a voltage which is proportional to theposition angle of the tail fin shaft 507. The sign of the voltage givesthe directional relationship with respect to the zero position of thetail fin shaft 507. The second arm of wiper 526 transfers this voltagevia the second track of potentiometer 525, which is the continuous stripof metal, to a pick-off terminal (not numbered) provided on thepotentiometer 525.

The tail fin shaft 507 is also shown to have mounted to it a drive cable530 which is connected via a turnbuckle 531 to the shaft 532 supportingthe vane 401A. The shaft 532 is mounted via a pair of duplex ballbearings 533, 534 to the support member 523. An end cap 535, which isshown to be attached to the shaft 532 by means of a screw 536, isprovided to retain the races of the duplex ball bearings 533. A shoulder537 is provided on the shaft 532 to retain the races of the duplex bailbearings 534. A seal between vane 401A and the support member 523 isprovided by means of a channel (not numbered) formed in the supportmember 523. Such channel is then filled with an “O” ring 538 to form ahot gas resistant seal.

The drive cable 530 between the shafts 507 and 532 here provides adirect one-for-one mechanical linkage between such shafts. Thus, forexample, a command from the seeker and autopilot 407 (FIG. 4A) toactuator 404A to rotate the missile tail 403A, say 10°, would result ina corresponding 10° rotation of the vane 401A. It will now beappreciated that the vanes 401A, 401B (FIG. 4) in the exhaust of therocket motor 402 (FIG. 4) (it being understood that another pair ofvanes is provided to make a cruciform control arrangement) are effectiveto provide the requisite control forces to initially control the flightof the intercepting missile 118 (FIG. 4) until such time as theintercepting missile 118 (FIG. 4) attains sufficient velocity for thetail surfaces 403A, 403B (FIG. 4) to become effective. The vanes 401A,401B are here designed to ablate so that when the flight of interceptingmissile 118 (FIG. 4) is being controlled by tail surfaces 403A, 403B(FIG. 4) little, if any, of the vanes 401A, 401B (FIG. 4) remains.

Referring now to FIG. 5A, the permanent magnetic field structure 550 ofthe basket rotor motor 401 (FIG. 5) here is shown to include fourradially fluxed, circular arc permanent magnets 503 (hereinafterreferred to simply as magnets 503). It is noted in passing that whilemagnets 503 are shown to be solid pieces, they could as well belaminated. The magnets 503 are made of samarium cobalt and are in theform of a sector of an annular cylinder. Such magnets are a product ofRaytheon Microwave and Power Tube Division, Waltham, Mass. The center ofeach sector lies on the circumference of a circle of radius R2 from thecenter of the field structure 550. Pole pieces 551 are shown to bebonded, in any conventional manner, to the inner surface of permanentmagnets 503. Each of pole pieces 551 is crescent-shaped, having at outerradius of R1 (the radius of the inner surface of the magnet sector) andan inner radius R3 (to overlie the basket rotor motor 501 (FIG. 5)).Each of pole pieces 503 subtends an angle A at the center of the fieldstructure 550 and is fabricated from a material having a highpermeability.

It is noted here in passing that, while the permanent magnetic fieldstructure 550 is shown to include four permanent magnets 503, inpractice the actual number of magnets can be any even number, dependingon the motor speed and torque required. Adjacent ones of the magnets 503are oppositely polarized and each of the magnets 503 is bonded to acommon housing 552 of a magnetic material, here magnetic steel, whichsupports the permanent magnets 503 and acts as a return path for themagnetic field between adjacent ones of the permanent magnets 503. Themagnetic circuit is completed by the concentric cylinder 517 (FIG. 5A).

If R2 is made equal to zero so that R1=R3 there would be no pole pieces551 and, under ideal conditions, the flux density in the air gap betweenthe permanent magnets 503 and the motor rotor 513′ (FIG. 5A) would begiven by:

$\begin{matrix}{{Bg} = {\frac{{Am} \cdot {Bm}}{Ag} = {Bm}}} & {{Eq}.\quad (1)}\end{matrix}$

where:

Bg=flux density in air gap (gauss)

Bm=flux density of magnet 503 (gauss)

Am=area of magnet 503 (cm²)

Ag=area of air gap (cm²)

Since an air gap is necessary for motor operation, the magnets 503cannot operate at their remanent flux density but must operate at somelower level determined by the intersection of the air gap line and thedemagnetization curve of the magnets 503. An additional loss of flux inthe air gap is attributable to high magnetic leakage. As is known, theuse of an iron pole piece has the effect of increasing the area of themagnet (Am) and, therefore, by making Am larger than the area of the airgap (Ag), air gap flux densities in excess of the remanent flux densityof the magnets 503 are theoretically possible.

Experiments conducted on a pair of magnets of constant diameterindicated that for a constant air gap, as the magnet length (L) isreduced, the flux density in the air gap drops off at a faster rate thanthat which would occur if only the demagnetizing curve of the magnet andits intersection with the air gap line were considered. The rapid dropoff in air gap flux density is attributable to low reluctance leakagepaths that exist around the magnet, i.e. from one face, over the edgesof the magnet to the face of the opposite polarity. If iron pole piecesare added to the magnets the leakage is even more pronounced since ironis a magnetically isotropic material and allows flux to emanate from thesides of the pole piece, resulting in a corresponding decrease in theflux in the air gap.

In the herein contemplated magnetic field structure 550 the flux densityin the air gap is optimized through the use of the crescent-shaped polepieces 551 as the sides (in the depth dimension) of the pole pieces 551are eliminated. Eliminating the sides of the pole pieces 551 increasesthe length of the leakage paths (because the magnets 503 areanisotropic) and also increases the leakage path reluctance (because theleakage surface area is reduced). Thus, by configuring the magnets 503in a circular arc of a radius that is smaller than the radius of thebasket rotor motor 501 (FIG. 5), the magnets 503 tend to shield theirpole pieces 551, thereby reducing the effect of magnetic leakage pathsand producing a higher flux density in the air gap between the basketrotor 513 (FIG. 5) and the magnets 503.

The magnetic field structure 550 is also shown to include the concentriccylinder 517 with windings 513′ appropriately disposed between the polepieces 551 and the concentric cylinder 517. As mentioned hereinabove,concentric cylinder 517 is here made of magnetic steel and has a highmagnetic permeability. The concentric cylinder 517 thus provides amagnetic return path allowing flux to flow from one pole piece 551through the windings 513′ and the concentric cylinder 517 to an adjacentpole piece 551.

Referring now to FIG. 6, missile launching station 106 is shown toinclude a number, here 24, of missile canisters 600 ₁, 600 ₂, . . . 600₂₄ arranged, as shown, such that missile canisters 600 ₁ to 600 ₁₂ areon the starboard side of naval vessel 100 (FIG. 1) and missile canisters600 ₁₃ to 600 ₂₄ are on the port side. Each of the missile canisters 600₁, 600 ₂ . . . 600 ₂₄ contains a missile (not shown) mounted on apneumatic ejection launcher (also not shown, but to be described indetail hereinafter with reference to FIG. 6A). The missile canisters 600₁, 600 ₂ . . . 600 ₂₄ are shown to receive command signals, here theMISSILE SELECT, FLIGHT MODE, INITIAL HEADING, and LAUNCH signals, fromradar control unit 301 (FIG. 3) via cables 603, 604, junction box 602and cable 601. The junction box 602 is included for purposes ofinstallation ease, so that cables are not required to be routed from theport to starboard sides of naval vessel 100 (FIG. 1). It is noted herein passing that, while interconnections are shown to be made onlybetween cables 603, 604 and the inboard ones of the missile canisters600 ₁, 600 ₂ . . . 600 ₂₄, in practice each of the starboard missilecanisters 600 ₁ to 600 ₁₂ are connected to cable 604 and each of theport missile canisters 600 ₁₃ to 600 ₂₄ are connected to cable 603.Again, to reduce the requisite amount of cabling between the missilecanisters 600 ₁, 600 ₂ . . . 600 ₂₄ and the radar control unit 301 (FIG.3), the identical command and heading signals are sent to each of themissile canisters 600 ₁, 600 ₂ . . . 600 ₂₄. However, the MISSILE SELECTsignal from radar control unit 301 (FIG. 3) is encoded in such a mannerthat only the rear receiver and decoder 406 (FIG. 4) of the desiredmissile will respond. The radar control unit 301 (FIG. 3) also supplies,via cables (not shown), an analog firing signal to the selected one ofthe missile canisters, such firing signal is effective to ignite anexplosive bolt (not shown but to be described hereinafter with referenceto FIG. 6A) located on the pneumatic ejection launcher (also not shown).

Referring now to FIG. 6A, an exemplary missile canister, here missilecanister 600 ₁, is shown to include a missile 610 and a pneumaticejection launcher 611 (hereinafter referred to simply as launcher 611).Positioned between the missile 610 and the launcher 611 is a guide rail612, which has a slot (not shown) formed in the center thereof forreasons which will be explained hereinbelow. The sides of the guide rail612 have “C-shaped” slots (not shown) formed therein for engagingcorresponding guide arms (also not shown) provided on the missile 610.

The pneumatic ejection launcher 611 is shown to include a hollow metalcylinder 613, a piston 614, an energy absorber 615 and a fill block 616.The fill block 616 is an annular-shaped block of metal, here steel,having a fill port 617 and an exhaust port 618 formed therein. The fillport 617 is connected via a valve (not shown) to an air compressor (alsonot shown) onboard the naval vessel 100 (FIG. 1). An “O” ring seal 619is provided, as shown, between the fill block 616 and the piston 614. Asecond “O” ring seal 620 is provided between the metal cylinder 613 andthe fill block 616 and is compressed by means of bolts (not shown)connecting the metal cylinder 613 to the fill block 616. An explosivebolt 621, which is here a Model No. 10630-1 from HOLEX, Inc., 2751 SanJuan Road, Hollister, Calif. 95023, is mounted, as shown, to the fillblock 616. The explosive bolt 621 is threaded into a tapped hole (notnumbered) in the fill block 616. The fill block 616 is mounted, in anyconventional manner, as by means of bolts (not shown), to a pedestal 622thereby compressing an “O” ring seal 623 provided, as shown, between thefill block 616 and the pedestal 622.

A thrust link 624, which extends through a slot (not numbered) providedin both the metal cylinder 613 and the guide rail 612, for engaging abuttress 625 provided on the missile 610 is located on the top of thepiston 614. A spring loaded pin (not shown), which engages the thrustlink 624, is also provided in the top of the piston 614, for reasonswhich will be explained in detail hereinafter.

In operation, the piston 614 is placed against the fill block 616 andheld in place by means of the explosive bolt 621, which also compressesthe “O” ring seal 619. The missile 610 is placed on the guide rail 612and slid toward the bottom of the missile canister 600 ₁ until thebuttress 625 on the missile 610 contacts the thrust link 624. The valve(not shown), which is connected between the fill port 617 and the aircompressor (also not shown), is opened and the piston 614 is charged.Upon receipt of a fire signal from the radar control unit 301 (FIG. 3),the explosive bolt 621 is severed at the break line 626 therebyreleasing the piston 614 and the missile 610. The reaction force of thecompressed air expanding from the piston 614 into the metal cylinder 613accelerates the piston 614 and the missile 610 forward. A pair of lowfriction wear rings 627 is provided on each end of the piston 614, whichallows the piston 614 to move freely inside the cylinder. An additional“O” ring (not numbered) is provided between the bottom pair of lowfriction wear rings 627. At the end of the piston stroke, the pistonhead (not numbered) impacts the energy absorber 615, which is here ablock of lead. The energy absorber 615 has a channel (not numbered)provided therein for receiving the thrust link 624 which is rotatablymounted in the piston 614. Once the thrust link 624 is forced within thechannel (not numbered) in the energy absorber 615, the spring loaded pin(not shown) within the piston 614 is released and retains the thrustlink 624 in the channel (not numbered) to prevent possible damage to themissile 610. As the energy absorber 615 is compressed, the piston 614 isstopped and the residual pressure in the cylinder 613 is bled off viathe exhaust port 618.

The missile canister 600 ₁ is prepared for reuse by removing the nowcompressed energy absorber 615 and the expended explosive bolt 621 fromthe pneumatic ejection launcher 611 and replacing them with new parts.The frangible cover 627 on top of the missile canister 600 ₁ is thenreplaced. It is noted here in passing that the sides (not numbered) ofthe missile canister 600 ₁ are fabricated from a honeycomb aluminummaterial in order to reduce the weight of the missile canister 600 ₁,and that the pneumatic ejection launcher 611 is rigidly affixed to oneside of the canister by means of bolts (not shown). Thus, with a secondcover (not shown) placed on the bottom of the missile canister 600 ₁, acertified round including the missile 610 and pneumatic ejectionlauncher 611 is thereby formed for shipping and storage purposes.

From the foregoing, it will be apparent to one of skill in the art thata point defense system according to this invention need not be limitedto its disclosed embodiment but may be deemed to include any shipboardpoint defense system utilizing any chosen radar system to detect andtrack both airborne and surface targets and to direct a verticallylaunched missile to intercept such targets. Further, it will be apparentthat mechanical details of the various novel elements disclosed may bechanged without departing from the inventive concepts disclosed anddescribed. It is felt, therefore, that this invention should not berestricted to its disclosed embodiment but rather should be limited onlyby the spirit and scope of the appended claims.

What is claimed is:
 1. For use on a naval vessel subjected to the actionof the sea, a combined search, navigational and tracking arrangementusing a single pulse radar to sense targets with a predeterminedspherical coordinate system defining a zone bottomed on the plane of theradar horizon about such vessel, such zone having an axis of symmetrycorresponding to a local vertical through such vessel, such radarincluding a phased array antenna and pulse forming means for generatingsuccessive pulses of radio frequency energy having equal lengths and forapplying each one of such successive pulses to the phased array antennato produce a beam illuminating the portion of the zone, such pulseforming means being arranged to produce, in accordance with apredetermined program, a first and a second part of each pulse withdifferent frequencies and different lengths.
 2. The arrangement as inclaim 1 wherein the pulse forming means is arranged to vary, inaccordance with a predetermined program, the repetition rate at whichsuccessive pulses are generated.